1. Field of the Invention
The present invention relates to a method for operating a mobile terminal as access point, wherein said access point composes a network together with one or more associated client stations, wherein said access point has an operational mode of alternating awake and sleep periods, and wherein said access point broadcasts beacon frames at regular intervals for signaling communication parameters to said associated client stations.
Furthermore, the invention relates to a mobile terminal, said terminal being operated as access point, wherein said access point composes a network together with one or more associated client stations, wherein said access point performs alternating awake and sleep periods, and wherein said access point broadcasts beacon frames at regular intervals for signaling communication parameters to said associated client stations.
2. Description of the Related Art
In recent years it has become commonly known to operate wireless or handheld devices, like e.g. mobile phones, laptops, cameras or tablets, in such a way that they act as access point (AP) in order to be able to make a one-to-one connection to a client terminal, or a group of several client terminals can connect simultaneously. Consequently, while traditionally the Wi-Fi technology has been mainly employed to provide internet connectivity by means of an access point serving a set of associated client stations, there is currently a trend in the Wi-Fi industry to consider every time more direct device to device connectivity.
A typical application scenario would be, for instance, a mobile terminal directly communicating, without the presence of an access point, to another mobile terminal, a printer, a digital camera or a display. One solution to this technical problem is to design devices that can support dual AP/client functionalities. In the following this technology is referred to as Soft-AP. According to this technology, a mobile terminal would act as a regular client in the presence of an access point, but when there is no access point present the mobile terminal would make itself appear as a traditional access point to establish communication with other devices, for instance a camera, a printer or a display.
Another possibility is to make use of the IBSS (Independent Basic Service Set) functionality—ad-hoc mode—defined in the IEEE 802.11 standard. However, a disadvantage of this approach in front of the Soft-AP solution is that many devices already existent in the market do not support the IBSS mode, for instance some Wi-Fi cameras. This problem does not exist in the Soft-AP solution because legacy devices simply see the Soft-AP mobile terminal as a traditional access point.
However, when the Soft-AP technology is applied to a mobile terminal a critical problem appears related to power consumption. In contrast to conventional stationary base stations, which are noncritical in terms of energy supply as they are constantly plugged to the power, in the case of mobile terminals the problem arises that they are typically battery-powered and, acting as access points, quickly drains the batteries of the devices. The reason is that the Wi-Fi protocol is designed based on the assumption that the access point is all the time awake and listening to the channel. Consequently, keeping the WLAN radio on results in a drastic reduction of battery time in the case of mobile terminals.
Therefore, all such devices need to be power efficient when acting as access points. However, setting a wireless terminal that acts as access point, e.g. as Wi-Fi access point, into a sleep state in order to save power, comes along with the risk of causing degradation on the Quality of Service (QoS) experienced by the connected clients. For example, switching the radio on and off has the risk of missing data packet transmissions in the uplink if the associated stations transmit data packets when the access point's radio is switched off. This heavily degrades user experience if some critical packets, for instance a TCP SYN initiating the connection to download a web page, are lost.